1. Field of the Invention
In some industrial and technical applications it is necessary to mix two or more liquids, each in the most exact possible proportion with respect to the others and in certain fields, like the pharmaceutical products industry and certain chemical operations involving reactions in which are critical the proportions of the reagents partaking in the reaction, the proportions must be maintained within minimum tolerances which can not be exceeded without the risk of having to discard the production.
When the batch mixing process is used, there is practically no problem of maintaining constant the proportions of the components of the batch, since it is comparatively easy to measure or weigh each of the components within minimum tolerances by methods already known in the art.
But when a continuous process is used, the problem may become really serious, since it is considerably more difficult to maintain constant the proportions of the components of the mixture during relatively long periods of operation of the machine.
It has already been proposed in the art to use a mixing apparatus, for at least two fluid components, which is provided with two storage tanks, one for each component, the respective liquid component being introduced in the storage tank until a certain level is reached, the liquidflowing by gravity from each tank to a mixer tank arranged below said storage tanks. Notwithstanding, the differences of level in the storage tanks, caused by the discharge of liquid from each tank and the replacement of the spent liquid, produce variations of the respective hydrostatics heads and thus introduce variations in the discharge flow rate from each storage tank; the mixture discharged from the mixer tank thus has a composition varying with time within limits which can be narrow comparatively considered, but which can be excessive in certain applications where a high accuracy is required. Another source of disturbance of the flow rates is the turbulence produced by the simultaneous charging and discharging of fluid into and from each storage tank.
This requires a continuous watch of the resulting composition and frequent manual readjustments in spite of which it can be necessary to discard some portions of the production, with the consequent economic losses.
One of the objects of this invention is to provide a metering and mixing apparatus for a plurality of liquids which, continuously operating, will maintain constant the proportions of the component liquids of the final mixture within considerably narrower limits than what is obtainable with the prior art apparatus.
A further object is to provide an apparatus of the kind mentioned that avoids turbulences in the liquid within each tank.
Another object is to provide an apparatus of the kind mentioned that is capable of maintaining the level of the liquid in each storage tank within predetermined maximum and minimum limits.
Another object is to provide an apparatus of the kind mentioned that provides a more effective mixing action of the component liquids.
Another object is to provide an apparatus of the kind mentioned capable of maintaining accurately the proportions of the component liquids during the entire working period and at the same time allowing to operate with high flow rates, that is to say with high production rates.
Another object is to provide an apparatus of the kind mentioned which has a construction which allows an easy cleaning of its components.
Another object is to provide an apparatus of the kind mentioned having means allowing a highly accurate desired adjustment, by means of a micrometrical adjustment device, of the flow rate of at least one of the streams forming the final mixture.